1. Field of the Invention
This invention relates to a heat-insulating engine with swirl chambers in an internal combustion engine.
2. Description of the Prior Art
In combustion chambers of internal combustion engines in general, a swirl chamber system incurs a greater loss of cooling water than a direct fuel injection system and its fuel cost performance is lower. However, since mixing of a fuel and air is effected twice, once in swirl chambers and another in main combustion chambers, in the swirl chamber system, the mixing state is better than in the direct fuel injection system. Further, generation quantities of NOx and HC are smaller in the swirl chamber system than in the direct fuel injection system and the amounts of smoke and particulates generated are also smaller. In connection with the formation process of soot, soot is more likely to occur when the fuel concentration is higher in a fuel-air mixture or its temperature is lower and as to the formation process of NOx, it is more likely to occur when the fuel concentration is lower in the fuel-air mixture or its temperature is higher. As to the formation process of HC, it is more likely to occur when the fuel concentration is lower in the fuel-air mixture or temperature is lower.
It can be understood from the explanations given above that in the internal combustion engines, the swirl chamber system is more advantageous than the direct fuel injection system in reducing the occurrence of soot, NOx and HC but the problem is yet left unsolved as to how to decrease the loss of cooling water in the swirl chamber system to a level equal to, or lower than, that in the direct fuel injection system. In other words, in order to accomplish the temperature rise during the rich mixture combustion period in the swirl chambers and to restrict the generation quantities of smoke and particulate intermediate products, particularly preferred for the swirl chambers of a Diesel engine is the structure which does not permit heat to radiate from its outer periphery, and in order to minimize the loss of cooling water and to improve the fuel economy, there remain the problems as to how to constitute the swirl chambers when they are constituted in the heat-insulating structure and how to secure the strength of the swirl chambers themselves.
Conventionally, the swirl chamber structure wherein the swirl chambers of an internal combustion engine are made of a ceramic material is disclosed in Japanese Utility Model Laid-Open Nos. 69324/1985, 44070/1980 and 48207/1979 and Japanese Patent Laid-Open Nos. 46317/1984 and 21508/1972, for example.
First of all, in the swirl chamber structure of the engine disclosed in Japanese Utility Model Laid-Open No. 69324/1985, swirl chamber forming members are made of a ceramic material and a metallic layer is formed on the inner wall surface of the swirl chambers of the swirl chamber forming members.
In the swirl chamber type combustion chambers of the Diesel engine disclosed in Japanese Utility Model Laid-Open No. 44070/1980, liners having the same shape as the inner surfaces of the combustion chambers and injection ports are formed along their inner surfaces, or a refractory material is sprayed to form a heat-insulating layer.
The swirl chamber forming members of the internal combustion engine disclosed in Japanese Utility Model Laid-Open No. 48207/1979 are produced by fitting a metallic ring having a compressive stress to the outer periphery of a ceramic material formed in a predetermined shape.
Furthermore, the combustion chamber components of the internal combustion engine disclosed in Japanese Patent Laid-Open No. 46317/1984 uses non-oxide ceramics of silicon type such as silicon nitride ceramics and silicon carbide ceramics as a blank material so that the surface of the non-oxide ceramics is converted to silicon oxide ceramics by high temperature heating and a thin layer of a precious metal catalyst is formed on the surface.
In the combustion chambers of the Diesel engine disclosed in Japanese Patent Laid-Open No. 21508/1972, part or the entire portion of the inner wall of the swirl chambers is made of a heat-insulating material and part or the entire portion of its outer periphery is reinforced by metal hoops.
The swirl chamber structure of the internal combustion engine disclosed in each of the prior art references described above cannot provide the sufficient effect in securing heat insulating property of the swirl chambers themselves. Sufficient heat-resistance and strength cannot be secured, either, against the thermal stress of the surface portion exposed to a combustion gas, and moreover, the prior art structure is not sufficient in securing mechanical strength of the swirl chamber structure. Thus, the prior art structures are not yet free from the serious problems.
In other words, in the structures described above where the swirl chambers are constituted by use of the ceramics described above as the heat-insulating material or as the heat-resistant material, it is extremely difficult to secure strength of the wall surface and to obtain sufficient heat-insulating characteristics. In order to obtain sufficient strength, the wall thickness of the ceramics must be increased, and even when the wall thickness of the ceramics is increased, a sufficient heat-insulating effect cannot be obtained.